TYPES OF BONES n LONG: humerus n SHORT: carpals n FLAT: frontal bone n IRREGULAR: vertebrae
Categorizing bones developmentally… n Endochondral –develop from pieces of cartilage deposited as sheets of tissue in embryo –Face, appendages n Dermal –Formed from sheets of fibrous connective tissue –Clavicle, scapula, flat cranial bones
n Alveolar –Teeth –Specialized groupings of bone cells n Sesamoid –Form within tendons due to stress on tendon –Patella, pisiform, various metacarpal, metatarsal bones
n Wormian –Small, irregular, isolated; develop within sutures
Periosteum “To surround the bone” Fibrous membrane, covers surface of the bone EXCEPT at the joint surfaces. Contains nerves and blood vessels Nutrition, sensation This is where the tendons & ligaments attach to the bone.
Yellow Marrow Red marrow spaces (surrounded by trabeculae)
Epiphysis At the end of each bone Made of cancellous or spongy bone Network of bone called trabeculae Spaces contain red marrow Site of hematopoiesis (blood cell production) Outer surface is compact bone Within joints, surfaces covered with hyaline articular cartilage
Epiphysial Plate n Also called the “growth plate”; –indicates that additional bone growth is possible n Site of bone elongation n Ossifies over time –then callled epiphysial line
Diaphysis “to grow apart” Hollow Tube Made of compact bone: organized into osteons Rigid but light
Medullary Cavity Hollow area inside diaphysis Bordered by spongy bone Lined by a thin membrane called the endosteum Capable of generating new bone cells Adults: contains soft, yellow bone marrow Mostly adipose tissue Food reserve for bone cells Children: more red marrow
Two kinds of bone Cancellous/Trabecular (Spongy) 80% of bone many spaces filled with marrow Compact (cortical) 20% of skeleton structure 80% of skeletal weight Structural unit = osteon
The OSTEON: Found in compact bone Matrix is organized into numerous structural units called osteons or Haversian systems. Consists of calcified matrix arranged in concentric rings called concentric lamellae
The Osteon The rings surround an opening called the Central (Haversian) Canal Canal contains blood, lymph vessels and nerves
The Osteon n Mature bone cells = osteocytes –Secrete bone matrix n Composed of collagen fibers and protein (osteocalcin) n The cell resides in a space called a lacuna n Canals, called canaliculi, connect the osteocytes to one another
More on the Osteon Nutrients pass from the blood vessel in the central canal through the canaliculi to the osteocytes
Classification: n Structural –Tissue composition, structural complexity –Cartilaginous, fibrous, synovial n Functional –Type of movement allowed –Synarthrotic, amphiarthrotic, diarthrotic
Bursa – Accessory Structure n Sac-like space made of fibrous tissue n Synovial fluid –thick, lubricating fluid –Nourishes, protects joints and surface –Secreted by epithelial cells n Found in articular areas where rubbing between skin, muscle, ligaments, or bones could occur n Can become inflamed/damaged = bursitis
Synarthrotic Joint (Immovable Joints) Fibrous Joint n Produce NO movement n Bone connected to bone by fibrous tissue n Purpose: to securely hold two bones together n Include –Sutures of the skull (synostoses/sutures) –Skull to teeth (gomphosis) –Tibia and fibula (syndemosis)
Amphiarthrotic Joint (Semi-movable) Cartilaginous n Bone connects to bone via cartilage n Allows slight movement n Includes –Pubic symphisis –Vertebrae
Diarthrotic/Synovial Joint n Allows much movement; joint cavity lined by synovial membranes n Some types –Ball & Socket: Shoulder, Hip –Hinge: Knee, Shoulder –Pivot: Atlas/Axis –Gliding: Between carpal bones, between tarsal bones –Saddle: thumb –Ellipsoid/Condyloid: wrist
Osteowhat? Osteoblasts secrete a mineralized matrix Once the osteoblast is surrounded by its matrix, it’s called an osteocyte, a bone cell. Osteoclasts break down bone. The first crystals of bone that form are pointed and needle-like: called spicules.
Ossification n Conversion of embryonic tissues into recognizable bone n 2 ways: –Endochondral n Long bones –Intramembranous n Flat bones –Combination – irregular bones
Ossification n Mesodermal cells form cartilage centers –Cartilage pegs form –Restructured, filled with hydroxylapatite (calcification) n Pegs formed by fibroblasts n Osteoblasts and osteoclasts sculpt growing bones
An osteoclast in action. Here an osteoclasts is eroding bone. The capsule formed by such action is called a Howship's capsule (H). Similar to the cell of the gut, osteoclasts have a ruffled border which increases the surface area for bone resorption.
Direction of Long Bone Growth n Epiphyseal plate made of hyaline cartilage is responsible for long bone growth. n The direction of growth is toward the diaphysis n The newly forming spongy bone (below the growth plate) is not clearly organized as the older spongy bone in the epiphysis above the growth plate.
n Fontanelles – soft spots –Regions of flat bone not fully ossified –Completed during teenage years
Fractures n Bone is cracked/splintered due to physical injury n Categorized by severity of break/angle at which break occurs
n Simple: –Crack in bone structure –May not be readily noticeable –Some large; may involve bleeding, pain, swelling –Greenstick fractures n One side frayed from fracture; other twisted, but not broken
n Compound/comminuted –Large fracture –One (more) area is displaced, shattered –Bleeding, swelling n Open –Tearing of skin occurs; easily infected
Angle of break n Transverse (horizontal) n Oblique (angle) n Spiral (twisted) n Angulation – bone changes overall shape n For healing to occur, blood accumulation must occur
Healing stages 1. Fracture 2. Granulation 3. Callus 4. Lamellar bone 5. Normal contour